Patent GB-649703-A (GB)
Title: Improvements relating to directional radio apparatus
IPC: G01S3/42
Filed: 1945-07-30
Abstract: 649,703. Automatic control systems. SPERRY GYROSCOPE CO., Inc. July 30, 1945, No. 19542. Convention date, July 29, 1944. [Class 38 (iv)] [Also in Groups XXXVIII and XL (c)] Relates to means for automatically stabilizing the elevation angle of a directional radio aerial which is mounted on an unstable platform, e.g. a -ship or aircraft. According to the invention, the aerial is rotatable about a normally horizontal " nod axis in a frame which is rotatable about a normally vertical " spin " axis on a supporting  structure and a gyro-vertical having a rotor case universally mounted about inner and outer gimbal axes in a casing, is mounted on the frame supporting the aerial about a normally horizontal axis parallel to the nod axis and normally parallel to one of the gimbal axes, a pick-off device being mounted about said gimbal axis whose output actuates a servo which positions the aerial and the casing about their respective axes so as to maintain the directivity axis of the aerial at a constant predetermined angle with the vertical. In Fig. 2 (side elevation) and Fig. 3 (plan view) a paraboloidal reflector 10 with a directive axis 11 is energized by a wave-guide 12. and is pivoted about a normally horizontal nod axis 14 on a yoke 13 which is rotatable about a normally vertical spin axis 15 for scanning in azimuth. A gyro-vertical is also mounted on the yoke 13, the gyro casing 18 being pivoted on a lateral axis 20 which is parallel to the nod axis 14 and intersects the spin axis 15 at right angles. The gyro casing is rigidly connected to a gear sector 31 which is also coupled to the reflector 10 by a link 30 so that the casing and reflector are maintained parallel and the sighting angle of the directive axis 11, in the angle A, Fig. 4, between the axis and the true vertical, is variable by a servomotor 32 which engages the gear sector 31, the servomotor being controlled by Selsyns 36 and 34, Fig. 8. Movement of the aerial about its nod axis 14 is limited by cams 40 and 41 on the gear sector 31 which operate switches in the input to the motor 32. The stators of the Selsyn transformer 36 are connected to the stators of the Selsyn transmitter 34 which is mounted on the gyro in such a manner that the direction of its stator field, and hence also the direction of the stator field of Selsyn 36, corresponds to the sighting angle of the reflector. When the rotor of Selsyn 36 is perpendicular to its stator field, no voltage is induced in the rotor, but when this neutral position is departed from due to movement either of the rotor control knob 37 or a change in the attitude of the aircraft a voltage is induced in the rotor which is applied through the amplifier 38 to operate the servomotor in such a manner as to restore the neutral position conditions. Thus the sighting angle of the reflector is set by the control 37 and is then automatically maintained independent of changes in attitude of the aircraft. If the nod axis 14 departs from its normal horizontal position by an angular amount C, Fig. 5, due to changes in the attitude of the aircraft, a bearing error B is produced defined by the relationship tan B=tan C x sin D, where D is complementary to the sighting angle A, Fig. 4, or if C and D can be limited to within 30 degrees by sin B=sin CxD. Means are shown in Fig. 8 for correcting this error in a.pulse radar system employing the above aerial system in which the echo signals are displayed by intensity modulation on a cathode-ray tube 51 with rectangular co-ordinates x and y representing range and bearing, the bearing deflection voltage being generated by a Selsyn system 48, 49. A further Selsyn system 44, 45 is provided, the Selsyn 44 being mounted on the gyro in such a manner that the output voltage from its rotor is the required function of the angle C and this voltage is applied across a potentiometer 42 whose spindle is ganged with the sighting angle control knob 37 and having a characteristic giving the required function of the angle D; hence the output from the potentiometer gives the required bearing correction voltage and this is combined with the output from Selsyns 48, 49. Gyroscope features. The gyro, Fig. 7 (plan view), comprises a rotor 22 with a vertical spindle mounted in a rotor case 21 which is pivoted about an inner axis 26 in a gimbal ring 23, the ring being pivoted about a perpendicular outer axis 27 in the gyro casing 18. The outer axis 27 is perpendicular to the axis 20 on which the gyro casing is pivoted so that the inner axis 26 is normally coincident with axis 20. Since the rotor spindle is normally coincident with the spin axis 15, the gyro is unaffected by centrifugal forces during azimuthal scanning. A known form of liquid level switch, Fig. 9 (not shown), may be mounted near the intersection of the inner and outer axes and centred on the spin axis to provide a suitable vertical reference and torque motors 28 and 29 of known form may be controlled by the switch to effect precession of the rotor case so as to maintain the spin axis vertical. The Selsyn 34 is mounted to detect relative tilt of the gyro casing and the rotor case about axis 20 and the Selsyn 44 detects relative movement of the gyro casing and gimbal ring about the outer axis.